Frequently Asked Questions


What is water pressure , bar and why would I need a pressure reducing valve?

Water supply network

The average water pressure is around 3 bar. The minimal water pressure your water company has to offer is 0.7. If that is the case you should have hydrofoor (a water pump)  installed to increase water pressure so the flow of water from your tap and shower is sufficient. A hydrofoor normally produces too much water pressure. So installing a pressure reducing valve set at 3 bar (optimal water pressure for all household appliances) is vitally important. Anything over 5 bar will damage your electrical appliances such as; the diswasher, electric water heater and your washing machine.

If you live in a house the water pressure downstairs will be higher than on the first floor. Besides that the water pressure can fluctuate per floor. For instance when you are using a lot of water in your kitchen the water pressure will fluctuate as a result of it. Logically you will have less water pressure in the bathroom on the first floor.

Electric water heater

Every water heater will have a maximum tank working pressure indicated in bar or mPa. This is the pressure building up inside the tank as a result of heating the water. So not the water pressure coming from your water mains.

Every single electric boiler (electric water heater) sold in the UK should comply with EU standards and is able to cope with a high water pressure for a short period of time. A boiler operating above the maximum working pressure for a longer period of time will get damaged. Therefore it is vitally important to use the right pressure relief valve. NEVER USE AN INCORRECT PRESSURE RELIEF VALVE. So please consult the manual of your electric water heater to find out what the maximum working pressure is for your product and use the supplied (or right) bar safety relief valve. The non-return valve inside the safety relief valve will prevent the water returning to the water mains from the electric water. So if you use an incorrect safety relief valve it will cause leakage and excessive calcification. An example: if you use an 8 bar pressure relief valve on a 6 bar maximum working pressure electric water heater the tank inside will build up excessive pressure (over the 6 bar maximum working pressure) leading to leakage from the tank (with a good chance of a short circuit) and excessive calcification inside the tank. So always use the right pressure relief valve.

Pressure relief valves for Lemet and Wesen electric water heaters

The pressure relief valve will kick into action releasing pressure by dripping water from that safety relief valve. For the Wesen the operating pressure is 8 bar, so if the pressure inside the tank builds up over 8 bar i twill release pressure through the pressure reliief valve. The Lemet electric water heaters have a 6 bar operating pressure, so anytime the pressure surpasses 6 bar the pressure relief valve will release the excess pressure.

Pressure reducing valve.

this is not a pressure relief valve but a valve that regulates pressure. The pressure reducing valve allows you to set the water pressure at 3 bar (the ideal water pressure) and it helps avoid water fluctuations. We recommend to always use a pressure reducing valve when you live in flat, apartment building, farm or live in an elevated area. Or if your company works from an industrial estate or old warehouse. A pressure reducing valve set at 3 bar will help avoid damage to your faucets, electric water heater, dishwasher and washing machine.

Apartment buidlng and flats

Often an apartment building or a flat will have a pump (a hydrofoor) to get the water up to the top floor. This can result in a water pressure of over 7 bar on the lower floors whilst the topfloor just has two bar water pressure. Another problem is fluctuation in water pressure when several people in your buliding use water. You can imagine that if the ground floor apartments use water at the same time there will be little water pressure on the top floor.

This can be damaging to your electric water heater and the other, before mentioned household appliances. Fluctuations will cause air bubbles to form inside the tank of the water heater eventually exposing the heating element to air causing it to overheat and short circuit.

The solution to avoid these issues is to install a pressure reducing valve. For an apartment building preferably on every floor where the water comes in. Or for a warehouse or normal house where the water mains enter your premises. A pressure reducing valve is the easy solution! (PAGE 8).


For more details regarding water pressure please consult the following links:


What can be fitted to the water mains?

Please check the website of the water company. There you will find datasheets with extensive calculations of what you can and cannot fit to the water mains.

Where is the template to mount the heater to the wall?

Please note, that usually only the smaller models (of up to 10 litres) do not have a wall mounting bracket as standard issue. A number of manufacturers do supply a template, that is printed on the box. This template allows you to easily mark where you need to drill holes to munt your water heater to the wall. Once you have drilled the holes place screw anchors in the holes and use proper screws to attach the water heater to the wall.

If the water heater does not have a template you need to measure the distance from the center of one mounting hole to the center of the other mounting hole. Or make your own cardboard template and use this to mark both mounting holes.  

How do I install a water heater?



Water heater


WRAS APPROVED 6 bar pressure relief valve ½”


 Unassembled UK plug



  • Preferably have your water heater fitted by a certified fitter
  • Make sure the stopcock on the mains water supply line is closed before commencing to install the water heater 
  • Unit must be installed vertically
  • Fit all components supplied
  • The water heater is not suitable for outdoor installation
  • It is forbidden to install the heater in places with explosion hazard, in a location with acid vapors and/or dust, or in gas-saturated environments or exposed to freezing temperatures, causing the freezing of water in the tank, in the places where the heater must be exposed to water vapor. In the case of the assembly, installation, and operation of the water heater in unusual places (e.g. in the attic, indoors in rooms with floors sensitive to water, in cabinets, etc.), it is necessary to take into account the possibility of the possible water leakage and in connection with that, take appropriate preventive measures enabling the connection of water and its drainage in order to prevent secondary damage.
  • High water pressure and/or fluctuating water pressure often occurs in apartment building, flats, farms, older houses and houses and buildings in elevated areas. High water pressure or fluctuating water pressure will damage your water heater. We therefore strongly advise you to install a pressure reducing valve if you live in a flat, apartment, older house, farm or in an elevated area. Install a pressure reducing valve where your mains water supply line enters your premises and set the water pressure at 3 bar. Any damage caused by a too high water pressure or fluctuating water pressure will not be covered by the warrantee. 


  1. Determine where you want to install your electric water heater and measure if the unit will fit in the space you’d like to install it. The place of mounting the heater must be compliant with its protection class and PN-HD 60364-7-701:1999. The installation must allow for an easy assembly and disassembly of the heater, without damaging the connections and the installation. Leave 30 cm of space underneath the water heater to allow easy access for servicing
  2. Ensure the wall is strong enough to support the water heater that will be filled with water. The heater must be installed using plugs and screws with sufficient lifting capacity and type adapted to the wall; two on each hanger.
  3. During the assembly, it is necessary to pay attention to the length of the power cord and the distance to the power socket.
  4. When installing the heater, it is necessary to pay special attention to the location of the pressure relief valve, so that the discharge of water from the pressure relief valve is uninterrupted.
  5. Measure and mark with a waterproof marker where you need to drill the holes for the plugs to mount the water heater. Before drilling the holes ensure the holes are level using a spirit level. Some water heaters come with a template to mark the holes. This template can be found either inside the box or is printed on the box.
  6. Drill holes, mount the plugs and fit the mounting bolts or screws (depending on the model).
  7. Place the electric water heater onto the wall. Make sure it is fitted securely.
  8. Tighten the mounting bolts or screws (depending on the model) solidly, so the electric water heater is flush against the wall.
  9. Cover ALL threaded fittings with Teflon tape to avoid water leakage. Turn the tape anti-clockwise onto the threaded fitting. Use teflon tape on the threaded fitting waterproofing the fitting. Some electric water heater brands have a special coating on the threaded fitting. You can easily remove this coating by using a wire brush and then use the teflon tape and cover the threaded fitting. NEVER remove the polyurethane foam inner layer of the electric water heater found on both the inlet and outlet of the electric water heater. This ensures the sealing of the electric water heater.
  10. Install the supplied pressure relief valve onto the cold water inlet side of the water heater (BLUE). Preferably directly onto the cold water inlet side, but never further than 2 metres away from the water heater. In any case DO NOT overtighten! IMPORTANT: Use ONLY the supplied 6 bar WRAS approved pressure relief valve! If you DO NOT use this pressure relief valve your guarantee will be void as a different pressure relief valve can damage the water heater.
  11. There may be a small amount of dripping (expansion water) from the pressure relief valve during the heating stage. This is completely normal. To allow this water to drain away uninterruptedly you have to create a discharge pipe (with or without a drain valve), facing downwards, directly below the pressure relief valve that leads to a drain. Place a Tee fitting below the pressure relief valve and either directly attach a discharge pipe or first a drain valve and then a discharge pipe. 
  12. You can opt to install an expansion vessel in between the water heater and the pressure relief valve to reduce water leakages from that pressure relief valve as much as possible.
  13. Always install pressure and temperature resistant water pipes to the mains water supply line. Connect both the hot water outlet and cold water inlet side of the electric water heater with these pipes. DO NOT overtighten the connectors as you can damage the connection causing water leakage.
  14. Fill the electric water heater with water by opening the warm water tap of your washbasin. Then gently open the water supply tap on the ‘BLUE’ side until it is fully opened.  Fill until it is full and there is no more air released from the warm water tap. Now close the warm water tap, keep the water supply tap fully open.
  15. Switch on the electric water heater by plugging in the power cable into the socket.
  16. Set your electric water heater to the desired water temperature using the analogue controller or digital display, depending on the model.
  17. Wait for your electric water heater to heat up. Depending on the size this can take several hours.
  18. If you want your electric water heater to last longer make sure you decalcify the heater every 2 to 2.5 years. Or as often as your manual suggests you to do so. Whilst decalcifying also replace the anode. Encrustation on the anode leads to unnecessary and unwanted energy consumption.
  19. Sometimes it is advisable to install a pressure reducing valve on the water-mains (by the main valve) to protect your water heater from fluctuating water pressure. Especially older buildings, farms and apartment building can suffer from fluctuating water pressure. Defects as a result of these fluctuations are not covered by the guarantee. 



The Lemet water heater operates with a working pressure of 6 bar. Always use the supplied WRAS approved 6 bar pressure relief valve. If you have it fitted by an installer please instruct your installer to use the supplied 6 bar pressure relief valve for the water heater to function properly and to avoid any problems. Moreover, if you do not use the supplied pressure relief valve your guarantee will become void.


The Wesen water heater operates with a working pressure of 8 bar. Always use the supplied WRAS approved 8 bar pressure relief valve. If you have it fitted by an installer please instruct your installer to use the supplied 8 bar pressure relief valve for the water heater to function properly and to avoid any problems. Moreover, if you do not use the supplied pressure relief valve your guarantee will become void.

Wesen: How do I install my Wesen water heater?

Please check the following video for instructions:

Wesen general installation

Wesen: my Wesen water heater is not working after installation. What is wrong?

If you have plugged in the power cord, before you have actually completed filling the water heater the thermal fuse will have been activated and have cut the power to the water heater (this is a safety precaution to protect the water heater).

It is very easy to reset the fuse: gently push the button on the fuse. You can find the fuse underneath the outer casing of the water heater.

Wesen: How does the power button work on my Wesen heater?

The big advantage of the Wesen water heater is that you can simultaneously switch on all heating elements by using the “Power” button. The heating elements in both tanks will be switched on speeding up the heating time.

Wesen Inox Flat Series:

Each model in this range has 2 heating elements. One double heating element in the first tank and one single heating element in the second tank.  

Distribution of power for the two separate tanks of the Inox Flat Series:

  • 30 to 50 litres, First tank: 2 x 700Watt / Second tank: 700Watt.

  • 80 to 100 litres, First tank: 2 x 800Watt / Second tank: 800Watt.

  • 150 to 200 litres, First tank: 2 x 1000Watt   / Second tank: 1000Watt

Wesen Silver Flat series:

The Wesen Silver Flat series has 2 single heating elements. One in each tank.

Distribution of power for the two separate tanks of the Inox Silver:

30 tot 100 litres, First tank: 700Watt / Second tank: 1300Watt

Lemet Ecoway: how do I alter the parameters in the menu?

In some cases it might be useful to alter the parameters. We urge you to do this only when absolutely necessary.

To enter the service menu to change these parameters take the following steps:

  • switch the power off, wait 10 minutes and switch the power back on again. Now switch the controller off (only the power indicator lights up)

  • Press and hold the “PROG” button until you see Fx yy appear (yy should blink) on your display

  • De x is the number of the parameter and the y the value

  • Press the up/down button to enter the desired value and confirm the set value with “OK”

  • IMPORTANT: If you change the parameters your ECO settings will be erased. These ECO settings will have to be reprogrammed.




Basic Settings


Anti legionella function  (0=off 1=on)




Repeat anti legionella

7-21 days

14 days


Start anti legionella function

0-23 hours

1 hour


Detection: no water in the tank 1=on 0=off




Anti-freeze function temperature

5-10 celsius

7 celsius


ECO mode level

35-45 celsius

45 celsius

Water pressure: does a high, fluctuating or low water pressure cause problems? And how do I solve this?

A high water pressure will cause too much pressure inside the tank and will damage your water heater 

Fluctuating water pressure or a low water pressure will lead to excessive calcification and create air bubbles inside the water tank. The heating element will be exposed to air causing the element to overheat. Eventually the heating element will crack exposing the electricity inside to water causing a short-circuit. 

All of this will lead to replacement of parts and a costly and avoidable repair.

The solution? A WRAS approved pressure reducing valve.  

The ideal water pressure for an electric water heater is 3 bar. Flats and apartment buildings often have a water pump to increase the water pressure so the water reaches every level with sufficient water pressure. This results in a too high a water pressure and/or fluctuating water pressure. Especially on the lower levels. That will cause damage, not only to your water heater, but also to your dishwasher and washing machine shortening their lifespan. 

Older buildings, houses and farms in mountainous areas often suffer from a low water pressure or fluctuating water pressure.

Please consult your water company and your installer about your water pressure and buy your WRAS approved pressure reducing valve. 

You can order the pressure reducing valve in our accessories and spare parts section:

Or you can order it as an extra when you order a water heater on our website. 

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